1. Field of the Invention
This invention relates to a novel color forming electrophotographic method utilizing a toner for electrostatic image containing a color forming agent (A) and a photoconductive photosensitive member or an image receiving sheet containing a color forming agent (B), and further to a particular electrophotographic material used therefor.
2. Description of the Prior Art
Heretofore, there have been known various electrophotographic processes such as those disclosed in U.S. Pat. No. 2,297,691, Japanese Patent Publication No. 23910/1967 and Japanese Patent Publication No. 24748/1968. In general, these electrophotographic processes comprise utilizing a photoconductive material, forming electric latent images on a photosensitive member, developing the latent images with a toner, if desired, transferring the developed image to an image receiving sheet such as paper and fixing the transferred image by heating or with solvent vapor.
It is widely known to use, as a developing toner, finely divided particles of 1 - 20 microns in diameter composed of a coloring pigment such as carbon black dispersed in a binder resin such as styrene resin. Such a toner is usually mixed with a carrier material such as glass beads, iron powder, fur and the like, or dispersed in an insulating liquid, and then attracted to or repulsed by the electrostatic latent image to visualize the negative or positive electric image.
The above-mentioned prior art has the following two problems. One is smudging during manufacturing and development since the toner is finely divided black powder. Such finely divided toner is so light that the toner is easily blown up to dirty remarkably hands, feet and clothes as well as room, and further to cause dust pollution outdoors. Dry toner is particularly of high contrast and gives images of high quality, but this dirt problem reduces the usefulness of dry toner.
The other is concerned with fixation. In general, toner is fixed by heating, but when a switch is turned on and then immediately the reproduction operation starts, fixation of the resulting image is incomplete and when rubbed, the toner is easily removed. Thus, the fixed portion is preliminarily heated and brought to a sufficient temperature, and then the reproduction operation can start. Particularly, a necessary preliminary heating time is usually 5 - 10 minutes for dry reproduction machine, and when once the machine is switched on, the fixing device should be kept at a constant temperature until the business time is finished.
As an electrophotographic method using a color forming system, there may be mentioned that disclosed in Japanese Patent Publication No. 15912/1966 which comprises covering a diazonium compound with wax and the like and combining with a paper coated with a coupler, that disclosed in Japanese Patent Publication No. 989/1967 and Japanese Patent Publication No. 3837/1970 which comprises using a volatile first chemical material as toner and a second chemical material (metal salt) as a reproduction sheet to form a colored image. However, when a diazonium compound is used as toner, there is disadvantageously a danger of explosion during pulverizing procedure and further and alkali treatment is necessary upon forming color, and therefore, it is not practical. Furthermore, in a system using a metal salt it is difficult to obtain clear and sharp color.